As a thin, high picture quality, and low power consumption display device, an organic EL (Electro Luminescence) display has been known. The organic EL display has a plurality of pixel circuits each including an organic EL element, a drive transistor, and a control transistor. As transistors in each pixel circuit, thin film transistors (hereinbelow, referred to as TFTs) are used.
In an organic EL display, variation occurs in a threshold voltage and a mobility of a drive transistor in a pixel circuit. Due to this, even when the same data potential is written to the pixel circuits, variation occurs in the amount of current flowing through the organic EL elements. Since the brightness of the organic EL element changes depending on the amount of current flowing through the organic EL element, when variation occurs in the amount of current flowing through the organic EL element, brightness unevenness occurs in a display screen. Therefore, to perform high-quality display in the organic EL display, a characteristic of the drive transistor has to be compensated. An organic EL display in which a characteristic of a drive transistor is compensated is described in, for example, Patent Document 1.
Another organic EL display has also been known in which all of organic EL elements emit light in the same period (for example, Patent Documents 2 and 3). In organic EL displays described in Patent Documents 2 and 3, at the head of one frame period, initialization is simultaneously performed to all of pixel circuits and threshold detection is simultaneously performed to all of the pixel circuits, next, data is sequentially written to the pixel circuits row by row, and organic EL elements included in all of the pixel circuits are made to emit light in the same period. FIG. 24 is a circuit diagram of a pixel circuit described in Patent Document 3. The pixel circuit illustrated in FIG. 24 includes TFTs 91 to 93, capacitors 94 and 95, and an organic EL element 96. The TFT 92 functions as a drive transistor.